Clinical Outcomes of Rescue Intracytoplasmic Sperm Injection at Different Timings Following in Vitro Fertilization

Background: although rescue intracytoplasmic sperm injection (r-icsi) is extensively used worldwide, the indication of r-icsi and its optimal timing remains obscure. this study aimed to assess the outcomes of r-icsi following in vitro fertilization in different timings when fertilization is confirmed. methods: this study included 5,156 cycles (47,785 eggs). fertilization was confirmed by polar body analysis after 4 and 6 hr of coincubation of the sperm and oocyte. oocytes that underwent ivf were divided into two groups based on the time when a second polar body was detected in more than 30% of all oocytes (four-hr group and six-hr group). if the second polar body was not detected or was present in less than 30% of all oocytes after six hr of coincubation, rescue-icsi (r-icsi) was performed for oocytes without a second polar body (r-icsi group). results: the fertilization rates of two pronuclear (2pn) oocytes in the three groups (four-hr group, six-hr group, and r-icsi group) were 70.7%, 51.3%, and 58.0%, respectively. the blastocyst formation rates were 62.8%, 53.4%, and 42.9%, respectively. conclusion: performing r-icsi after six hr of coincubation can salvage cases with fertilization failure in ivf. the higher fertilization rate of r-icsi indicates that all oocytes without signs of fertilization after six hr of coincubation should undergo r- icsi.